A variety of disorders, including autism, schizophrenia, achondroplasia, Apert Syndrome, and some cancers are more common in those born to older fathers. This association has been referred to as the paternal age effect (PAE). High-throughput, low-cost DNA sequencing techniques have recently yielded very large numbers of candidate de novo alleles in some of these diseases (e.g., autism and schizophrenia). Positive selection of mutant spermatogonial stem cells (SSCs) in the human testis may enable aberrant sperm to contribute such de novo mutant alleles to the next generation, resulting in the observed pathology. We are addressing this hypothesis by manipulating adult SSCs in culture, in conjunction with transplantation in vivo, in order to provide direct, experimental evidence for a putative mechanism of PAEs. The goals of the project are to address the mechanisms of specific disease-associated mutations and develop a protocol to discover and rapidly validate novel mutations. In order to design strategies to prevent or treat inherited disorders, an understanding of their molecular origins will be extremely valuable. The experiments described herein would support a common mechanism for PAEs and would show that PAE diseases could be considered prototypical stem cell-based diseases. An in vitro modeling approach to mutant allele discovery could eventually overcome some of the technical barriers to identification of genetic lesions associated with multigenic PAE diseases (e.g., autism), which otherwise requires large human data sets. By improving our understanding of the cellular basis for PAE disease pathogenesis and the roles of discrete mutations, experimental manipulation of SSCs could lead directly to novel therapeutic strategies for patients.